Various unsaturated hydrocarbon polymers have been reacted with maleic anhydrides to form a variety of maleic anhydride adducts of unsaturated hydrocarbon polymers. The reactivity of maleic anhydride with many unsaturated hydrocarbon polymers is poor and, in some instances, as for example with EPDM rubber, even employment of extensive heating is ineffective. Free radical reactions which graft maleic anhydride onto the unsaturated hydrocarbon polymer have been utilized as alternative routes. Free radical grafting leads to chain scission, crosslinking, grafting onto oils or other paraffinic solvents. The reaction of sulfomaleic anhydride with the unsaturated hydrocarbon polymer overcomes these aforementioned deficiencies in that the sulfomaleic anhydride can be reacted with the unsaturated hydrocarbon polymer at moderate temperatures in either the bulk or solution state without the employment of free radical initiators. Utilizing the resultant adduct of sulfomaleic anhydride with unsaturated hydrocarbons, polar molecules can be covalently bonded through the anhydride group by reacting the resultant adduct with a a polyamine compound and simultaneously therewith, or alternatively thereto, the sulfonic acid group of the resultant adduct can be neutralized with an organic amine, polyamine or metal counterion. In the case of neutralization of the sulfonic acid group the resulting adduct is an ionomer, a polymer which contains physical links, which is capable of being reprocessed.